A cartridge packages a bullet, propellant, and a primer into a single metallic case which is dimensioned precisely to be fired from a given caliber weapon. The cartridge primer is usually in the form of a small metallic cup, about 4 to 6 mm in diameter, which cup is friction fit within a rearwardly open metal bore formed in the base of the cartridge case. Typically, the cartridge primer contains a precise quantity of impact or pressure sensitive explosive material which is packed in place and covered by a thin paper disc, over which is fitted a single or grouping of metallic sections which function as an anvil—such that when the pressure sensitive explosive material is subjected to a physical force, such as that created between a firing pin and the anvil, the shock detonates the sandwiched explosive material which—in turn—expels hot gases up a channel within the base of the cartridge, igniting a booster capsule or pellet within that channel. The combined explosive effect of the primer and the booster pellet ignites the propellant contained in the body of the cartridge, which generates significant hot, rapidly expanding gases, thereby propelling the bullet from the cartridge and from the weapon.
Unfortunately, the pressure sensitive explosive materials use in primers, are hazardous or otherwise environmentally “unfriendly,” such as lead styphnate, lead azide, mercury (II) fulminate, potassium perchlorate, or diazodinitrophenol (DDNP). Prior attempts to reduce or substitute less hazardous or more environmentally friendly material have met with limited success, due—in part—to the fact that proposed substitute pressure sensitive materials, such as metastable interstitial composite (MIC) disclosed in U.S. Pat. No. 5,717,159 (comprising an oxidizer, such as molybdenum trioxide, and a fuel, such as nano-sized aluminum powder), does not produce sufficient gas upon combustion to perform effectively in existing medium caliber cartridges under cold conditions. Specifically, it has been found in the case of medium caliber, e.g. 25 mm cartridges, under cold conditions, the MIC of U.S. Pat. No. 5,717,159 fails to generate sufficient gas upon combustion to achieve an acceptable firing action time, i.e. a cycle time of less than the 6 milliseconds, the standard set by the U.S. Army. In fact, the U.S. Army standard requires this less than 6 millisecond action time at temperatures as low as −65 degrees Fahrenheit—a temperature at which such MIC primer materials uniformly fail to achieve the required action standard. Failure to achieve such an action time can potentially cause severe accidents, due to the internal ballistics within the barrel, when a subsequent bullet is fired too soon after a delayed prior bullet.
It is important to note that the less than 6 millisecond action time discussed above is a limitation required of 100% of the fielded cartridges. This means that any manufacturer of such bullets must utilize a primer for their cartridges that will meet this requirement, at all temperature ranges, repeatable. The particular primer disclosed and claimed herein, does meet the subject action standard criteria, repeatable, 100% of the time, even at very low temperatures.
Therefore there is a need in the art for an environmentally friendly, MIC based primer for medium caliber cartridges that will meet the action standard time repeatedly, especially under extremely cold conditions.